What is the best C Skill to give to Soleil?

I currently have Even Speed Wave on my 45 speed Soleil. It allows her to hit 51 on even turns and gives an ally +6 speed if they're next to her. She uses Flashing Blade as her SS, so it works out.

Another skill you could use is Odd Attack Wave. She's got pretty high attack, even without an Attack Boon.

This is the Soleil that I'm building up right now, haven't tried her in arena right now, but she is very usefull in GHBs since she is able to engage multiple fight in one turn

My Soleil is +4 and has Odd Atk Wave. It really depends though on what phase you have her specialize in.

i usually have my soleil dive in headfirst so i put atk smoke on her with hardy bearing